linux-kernel - [PATCH V2 15/20] dmaengine/amba-pl08x: Align lli

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Message-ID: <aa50fd324708557b6e904da8f62a567bb54c9dd8.1312190881.git.viresh.kumar@st.com>
Date:	Mon, 1 Aug 2011 15:07:25 +0530
From:	Viresh Kumar <viresh.kumar@...com>
To:	<linus.walleij@...aro.org>
Cc:	<vinod.koul@...el.com>, <dan.j.williams@...el.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux@....linux.org.uk>,
	<armando.visconti@...com>, <shiraz.hashim@...com>,
	<vipin.kumar@...com>, <rajeev-dlh.kumar@...com>,
	<deepak.sikri@...com>, <vipulkumar.samar@...com>,
	<amit.virdi@...com>, <viresh.kumar@...com>,
	<pratyush.anand@...com>, <bhupesh.sharma@...com>,
	<viresh.linux@...il.com>
Subject: [PATCH V2 15/20] dmaengine/amba-pl08x: Align lli_len to max(src.width, dst.width)

Currently lli_len is aligned to min of two widths, which looks to be incorrect.
Instead it should be aligned to max of both widths.

Lets say, total_size = 441 bytes

MIN: lets check if min() suits or not:

CASE 1: srcwidth = 1, dstwidth = 4
min(src, dst) = 1

i.e. We program transfer size in control reg to 441.
Now, till 440 bytes everything is fine, but on the last byte DMAC can't transfer
1 byte to dst, as its width is 4.

CASE 2: srcwidth = 4, dstwidth = 1
min(src, dst) = 1

i.e. we program transfer size in control reg to 110 (data transferred = 110 * srcwidth).
So, here too 1 byte is left, but on the source side.

MAX: Lets check if max() suits or not:

CASE 3: srcwidth = 1, dstwidth = 4
max(src, dst) = 4

Aligned size is 440

i.e. We program transfer size in control reg to 440.
Now, all 440 bytes will be transferred without any issues.

CASE 4: srcwidth = 4, dstwidth = 1
max(src, dst) = 4

Aligned size is 440

i.e. We program transfer size in control reg to 110 (data transferred = 110 * srcwidth).
Now, also all 440 bytes will be transferred without any issues.

Signed-off-by: Viresh Kumar <viresh.kumar@...com>
Acked-by: Linus Walleij <linus.walleij@...aro.org>
---
 drivers/dma/amba-pl08x.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c
index 0bdf3b8..ef02fb9 100644
--- a/drivers/dma/amba-pl08x.c
+++ b/drivers/dma/amba-pl08x.c
@@ -666,20 +666,22 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x,
 		 * width left
 		 */
 		while (bd.remainder > (mbus->buswidth - 1)) {
-			size_t lli_len, tsize;
+			size_t lli_len, tsize, width;
 
 			/*
 			 * If enough left try to send max possible,
 			 * otherwise try to send the remainder
 			 */
 			lli_len = min(bd.remainder, max_bytes_per_lli);
+
 			/*
-			 * Check against minimum bus alignment: Calculate actual
+			 * Check against maximum bus alignment: Calculate actual
 			 * transfer size in relation to bus width and get a
-			 * maximum remainder of the smallest bus width - 1
+			 * maximum remainder of the highest bus width - 1
 			 */
-			tsize = lli_len / min(mbus->buswidth, sbus->buswidth);
-			lli_len	= tsize * min(mbus->buswidth, sbus->buswidth);
+			width = max(mbus->buswidth, sbus->buswidth);
+			lli_len = (lli_len / width) * width;
+			tsize = lli_len / bd.srcbus.buswidth;
 
 			dev_vdbg(&pl08x->adev->dev,
 				"%s fill lli with single lli chunk of "
-- 
1.7.2.2

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